JSFiddle - React, Tailwind, and code Playground

HTML

<div id="block1"></div>
<div id="block2"></div>

CSS

#block1 {
    display: block;
    width: 100px;
    height: 100px;
    background: green;
}

#block2 {
    display: none;
    width: 100px;
    height: 100px;
    background: red;
}

#block1:hover + #block2 {
    display: block;
}